knock down vs strike

knock down is not a noun while strike is a noun.

Word	Noun	Adjective	Verb	Adverb
knock down	No	No	Yes	No
strike	Yes	No	Yes	No

As verbs, strike is a hypernym of knock down; that is, strike is a word with a broader meaning than knock down:

knock down (noun)	strike (noun)
	a group's refusal to work in protest against low pay or bad work conditions
	a score in tenpins: knocking down all ten with the first ball
	an attack that is intended to seize or inflict damage on or destroy an objective
	a conspicuous success
	(baseball) a pitch that the batter swings at and misses, or that the batter hits into foul territory, or that the batter does not swing at but the umpire judges to be in the area over home plate and between the batter's knees and shoulders
	a gentle blow

knock down (verb)	strike (verb)
shatter as if by explosion	cause to form (an electric arc) between electrodes of an arc lamp
knock down with force	arrive at after reckoning, deliberating, and weighing
cause to come or go down	indicate (a certain time) by striking
	make a strategic, offensive, assault against an enemy, opponent, or a target
	deliver a sharp blow, as with the hand, fist, or weapon
	hit against; come into sudden contact with
	affect or afflict suddenly, usually adversely
	produce by manipulating keys or strings of musical instruments
	remove by erasing or crossing out or as if by drawing a line
	pierce with force
	smooth with a strickle
	hook by a pull on the line
	produce by ignition or a blow
	form by stamping, punching, or printing
	disassemble a temporary structure, such as a tent or a theatrical set
	have an emotional or cognitive impact upon
	drive something violently into a location
	occupy or take on
	cause to experience suddenly
	find unexpectedly
	stop work in order to press demands
	attain
	touch or seem as if touching visually or audibly